U.S. patent number 7,233,082 [Application Number 10/731,879] was granted by the patent office on 2007-06-19 for interconnecting power generation system.
This patent grant is currently assigned to Ebara Densan Ltd.. Invention is credited to Tai Furuya, Seiichi Ishihara, Tadashi Kataoka, Noboru Kinoshita, Eishi Marui, Terence McKelvey, Takahide Ozawa, Motoyasu Sato, Shaojun Zheng.
United States Patent |
7,233,082 |
Furuya , et al. |
June 19, 2007 |
**Please see images for:
( Certificate of Correction ) ** |
Interconnecting power generation system
Abstract
To provide an interconnecting power generation system which can
detect an abnormality in the utility power supply and can be
isolated from a utility power system and can prevent damage to a
turbogenerator. An interconnecting power generation system
comprises: an interconnecting inverter 14; a voltage phase shift
circuit 20 which synchronizes the output voltage phase of the
interconnecting inverter 14 with the utility power voltage phase
and monitors zero crossings of the utility power voltage, and which
shifts the output voltage phase from the utility power voltage
phase and shifts the shifted output voltage phase to the utility
power voltage phase; a phase comparator 24 for comparing the
voltage phase of the utility power system 10 and the output voltage
phase of the interconnecting inverter; and an interconnection
control unit 30 which detects a power outage caused by an
interruption of power supply from the utility power system 10 based
on a series of a predetermined number of matching signals outputted
from the phase comparator 24 and sends a control signal to a
circuit breaker 22 to shut off the output of the interconnecting
inverter 14 from the utility power system 10.
Inventors: |
Furuya; Tai (Tokyo,
JP), Kataoka; Tadashi (Tokyo, JP),
McKelvey; Terence (Tokyo, JP), Marui; Eishi
(Tokyo, JP), Sato; Motoyasu (Fujisawa, JP),
Ozawa; Takahide (Fujisawa, JP), Zheng; Shaojun
(Fujisawa, JP), Ishihara; Seiichi (Fujisawa,
JP), Kinoshita; Noboru (Fujisawa, JP) |
Assignee: |
Ebara Densan Ltd. (Tokyo,
JP)
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Family
ID: |
32500871 |
Appl.
No.: |
10/731,879 |
Filed: |
December 9, 2003 |
Prior Publication Data
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Document
Identifier |
Publication Date |
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US 20040264089 A1 |
Dec 30, 2004 |
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Foreign Application Priority Data
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Dec 10, 2002 [JP] |
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2002-357778 |
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Current U.S.
Class: |
307/64 |
Current CPC
Class: |
H02J
3/38 (20130101); H02J 3/388 (20200101) |
Current International
Class: |
H02J
7/00 (20060101); H02J 9/00 (20060101) |
Field of
Search: |
;307/64 |
References Cited
[Referenced By]
U.S. Patent Documents
Foreign Patent Documents
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6-38696 |
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Apr 1989 |
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JP |
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3142029 |
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Apr 1994 |
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JP |
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3127250 |
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Jan 1995 |
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JP |
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PCT/JP2003/010564 |
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Aug 2002 |
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WO |
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Primary Examiner: Jackson; Stephen W.
Assistant Examiner: Amaya; Carlos
Attorney, Agent or Firm: The Webb Law Firm
Claims
What is claimed is:
1. An interconnecting power generation system connected in parallel
to a utility power system for supplying electrical power to an
interconnecting load, comprising: an interconnecting inverter for
linking generated electrical power to said utility power system; a
voltage phase shift circuit which synchronizes the output voltage
phase of said interconnecting inverter with the utility power
voltage phase and monitors zero crossings of said utility power
voltage, and which, when a predetermined number of zero crossings
have been detected, to detect a power outage actively, shifts said
output voltage phase from said utility power voltage phase during
one cycle and shifts the shifted output voltage phase to said
utility power voltage phase during the following cycle; a circuit
breaker for shutting off the output of said interconnecting
inverter from said utility power system; a phase comparator for
comparing the voltage phase of said utility power system and said
output voltage phase of said interconnecting inverter; and an
interconnection control unit which detects a power outage caused by
an interruption of power supply from said utility power system
based on a series of a predetermined number of matching signals
outputted from said phase comparator and sends a control signal to
said circuit breaker to shut off the output of said interconnecting
inverter from said utility power system.
2. An interconnecting power generation system connected in parallel
to a utility power system for supplying electrical power to an
interconnecting load, comprising: an interconnecting inverter for
linking generated electrical power to said utility power system; a
voltage phase shift circuit which synchronizes the output voltage
phase of said interconnecting inverter with the utility power
voltage phase and monitors zero crossings of said utility power
voltage, and which, when a predetermined number of zero crossings
have been detected, shifts said output voltage phase from said
utility power voltage phase during one cycle and shifts the shifted
output voltage phase to said utility power voltage phase during the
following cycle; a circuit breaker for shutting off the output of
said interconnecting inverter from said utility power system; a
phase comparator for comparing the voltage phase of said utility
power system and said output voltage phase of said interconnecting
inverter; and an interconnection control unit which detects a power
outage caused by an interruption of power supply from said utility
power system based on a series of a predetermined number of
matching signals outputted from said phase comparator and sends a
control signal to said circuit breaker to shut off the output of
said interconnecting inverter from said utility power system;
wherein, when no matching signal is outputted from said phase
comparator within a period during which said output voltage phase
is to be matched with said utility power voltage phase, said
interconnection control unit detects variations in the frequency of
said utility power system and sends a control signal to said
circuit breaker to shut off the output of said interconnecting
inverter from said utility power system.
3. An interconnecting power generation system connected in parallel
to a utility power system and for supplying electrical power to an
interconnecting load, comprising: a turbogenerator for generating
electrical power, an interconnecting inverter for linking
electrical power generated by said turbogenerator to said utility
power system; a voltage phase shift circuit which synchronizes the
output voltage phase of said interconnecting inverter with the
utility power voltage phase and monitors zero crossings of said
utility power voltage, and which, when a predetermined number of
zero crossings have been detected, shifts said output voltage phase
from said utility power voltage phase during one cycle and shifts
the shifted output voltage phase to said utility power voltage
phase during the following cycle; a circuit breaker for shutting
off the output of said interconnecting inverter from said utility
power system; a phase comparator for comparing the voltage phase of
said utility power system and said output voltage phase of said
interconnecting inverter; and an interconnection control unit which
detects a power outage caused by an interruption of power supply
from said utility power system based on a series of a predetermined
number of matching signals outputted from said phase comparator and
sends a control signal to said circuit breaker to shut off the
output of said interconnecting inverter from said utility power
system, and which decreases the rotational speed of said
turbogenerator to a predetermined speed during the period between
the detection of said power outage and the shutoff of said utility
power system.
4. The interconnecting power generation system according to claim
3, wherein said turbogenerator recharges a battery within said
predetermined period of time in response to said shutoff
command.
5. An interconnecting power generation system connected in parallel
to a utility power system and for supplying electrical power to an
interconnecting load, comprising: a turbogenerator for generating
electrical power, an interconnecting inverter for linking
electrical power generated by said turbogenerator to said utility
power system; a voltage phase shift circuit which synchronizes the
output voltage phase of said interconnecting inverter with the
utility power voltage phase and monitors zero crossings of said
utility power voltage, and which, when a predetermined number of
zero crossings have been detected, shifts said output voltage phase
from said utility power voltage phase during one cycle and shifts
the shifted output voltage phase to said utility power voltage
phase during the following cycle; a circuit breaker for shutting
off the output of said interconnecting inverter from said utility
power system; a phase comparator for comparing the voltage phase of
said utility power system and said output voltage phase of said
interconnecting inverter; and an interconnection control unit which
detects a power outage caused by an interruption of power supply
from said utility power system based on a series of a predetermined
number of matching signals outputted from said phase comparator and
sends a control signal to said circuit breaker to shut off the
output of said interconnecting inverter from said utility power
system, and sends a shutoff command to said turbogenerator to stop
the operation of said turbogenerator after allowing the turbine to
rotate at the rated rotational speed for a predetermined period of
time.
6. The interconnecting power generation system according to claim
5, wherein said turbogenerator recharges a battery within said
predetermined period of time in response to said shutoff command.
Description
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates to an interconnecting power generation
system and, more particularly, to an interconnecting power
generation system for supplying electrical power to an
interconnecting load in conjunction with a utility power
system.
2. Description of the Related Art
In general, an interconnecting power generation system comprises an
inverter apparatus for converting a DC output of a solar power
generation system for example as a DC power source into an AC
output and linking the DC power source to an AC utility power
supply. A control unit for controlling the inverter apparatus has a
detection circuit for detecting the phase voltage of the utility
power supply, a detection circuit for detecting the output current
of the inverter apparatus, an arithmetic circuit for calculating
the error between signals indicating the phase voltage of the
utility power supply and the output current of the inverter
apparatus detected by the respective detection circuits, and a
driver circuit for controlling the switching of the inverter
apparatus based on the output of the arithmetic circuit, and makes
the output current outputted from the current-controlled inverter
apparatus follow the phase voltage signal of the utility power
supply so that a sine wave current coincident in phase with the
voltage of the utility power supply can be outputted. The
interconnecting power generation system thereby converts electrical
power generated by a solar cell into AC electrical power for
example.
However, in order to interrupt power supply in a utility power
system intentionally for maintenance or inspection, a switch
upstream of the power outage section must be opened to interrupt
the power supply to the section. When an interconnecting power
generation system described as above is installed in or connected
to the power outage section, it is necessary to detect the power
outage and open a switch interposed between the interconnecting
power generation system and the utility power system to isolate the
interconnecting power generation system from the utility power
system.
When an abnormality in the utility power supply such as an
over-frequency or under-frequency condition is detected, the
interconnecting power generation system must be isolated from the
utility power system by opening the switch.
Moreover, in an interconnecting power generation system comprising
a turbogenerator, at the moment when the interconnecting power
generation system is isolated from the utility power system, the
generator is put into a no-load operating condition to the
rotational speed of the turbine rapidly increase to exceed the
absolute rated speed, resulting in damage to the turbine or the
auxiliaries.
The present invention has been made in view of the above
circumstances and it is, therefore, an object of the present
invention to provide an interconnecting power generation system
which can detect an abnormality in the utility power supply and can
be isolated from the utility power system and can prevent damage to
a turbogenerator.
SUMMARY OF THE INVENTION
To achieve the above object, according to a first aspect of the
invention, as shown for example in FIG. 1, there is provided an
interconnecting power generation system 1 connected in parallel to
a utility power system 10 for supplying electrical power to an
interconnecting load 12, comprising: an interconnecting inverter 14
for linking generated electrical power to the utility power system
10; a voltage phase shift circuit 20 which synchronizes the output
voltage phase of the interconnecting inverter 14 with the utility
power voltage phase and monitors zero crossings of the utility
power voltage, namely points at which the utility power voltage
(alternating voltage waveform) crosses the zero-volt line, and
which, when a predetermined number of zero crossings have been
detected or when a zero crossing of the utility power voltage is
detected after an internal timer has reached a predetermined period
of time, with the zero crossing timing as a starting point, shifts
the output voltage phase from the utility power voltage phase
during one cycle and shifts the shifted output voltage phase to the
utility power voltage phase during the following cycle; a circuit
breaker 22 for shutting off the output of the interconnecting
inverter 14 from the utility power system 10; a phase comparator 24
for comparing the voltage phase of the utility power system 10 and
the output voltage phase of said interconnecting inverter 14; and
an interconnection control unit 30 which detects a power outage
caused by an interruption of power supply from the utility power
system 10 based on a series of a predetermined number of matching
signals outputted from the phase comparator 24 and sends a control
signal to the circuit breaker 22 to shut off the output of the
interconnecting inverter 14 from the utility power system 10.
Further, the phase is shifted reliably for a period of two cycles
of an advanced phase and a delayed phase, with the zero crossing
timing as a starting point. Thus, when a power outage in the
utility power system occurs, for example, in contrast to the case
where the phase is shifted to be advanced only for one cycle, which
may result in the phase not to be shifted if the phase is
oppositely shifted to be delayed according to the load condition
and may result in the inability to detect the power outage, the
interconnection control unit 30 can detect the power outage
irrespective of the load condition using the comparison result of
the phases during the period of two cycles of the advanced phase
and the delayed phase. Namely, the interconnection control unit 30
can detect certainly the power outage in the second cycle even if
the phase is delayed according to the load condition.
In the interconnecting power generation system configured in this
way, the interconnection control unit 30 can detect a power outage
caused by an interruption of power supply from the utility power
system 10 based on a series of the predetermined number of matching
signals outputted from the phase comparator 24 and send a control
signal to the circuit breaker 22 to shut off the output of the
interconnecting inverter 14 from the utility power system 10.
To achieve the above object, according to a preferred embodiment of
the first aspect, there is provided an, wherein, as shown for
example in FIG. 1, when no matching signal is outputted from the
phase comparator 24 within a period during which the output voltage
phase is to be matched with the utility power voltage phase, the
interconnection control unit 30 detects variations in the frequency
of the utility power system 10 and sends a control signal to the
circuit breaker 22 to shut off the output of the interconnecting
inverter 14 from the utility power system 10.
In the interconnecting power generation system configured in this
way, the interconnection control unit 30 can detect variations in
the frequency of the utility power system 10 and can shut off the
output of the interconnecting inverter from the utility power
system 10 by sending a control signal to the circuit breaker
22.
To achieve the above object, according to a second aspect of the
invention, as shown for example in FIG. 1, there is provided an
interconnecting power generation system 1 connected in parallel to
a utility power system 10 and for supplying electrical power to an
interconnecting load 12, comprising: a turbogenerator 32 for
generating electrical power, an interconnecting inverter 14 for
linking electrical power generated by the turbogenerator 32 to the
utility power system 10; a voltage phase shift circuit 20 which
synchronizes the output voltage phase of the interconnecting
inverter 14 with the utility power voltage phase and monitors zero
crossings of the utility power voltage, and which, when a
predetermined number of zero crossings have been detected, shifts
the output voltage phase from the utility power voltage phase
during one cycle and shifts the shifted output voltage phase to the
utility power voltage phase during the following cycle; a circuit
breaker 22 for shutting off the output of the interconnecting
inverter 14 from the utility power system 10; a phase comparator 24
for comparing the voltage phase of the utility power system 10 and
the output voltage phase of the interconnecting inverter; and an
interconnection control unit 30 which detects a power outage caused
by an interruption of power supply from the utility power system 10
based on a series of a predetermined number of matching signals
outputted from the phase comparator 24 and sends a control signal
to the circuit breaker 22 to shut off the output of the
interconnecting inverter 14 from the utility power system 10, and
which decreases the rotational speed of the turbogenerator 32 to a
predetermined speed during the period between the detection of the
power outage and the shutoff of the utility power system 10.
In the interconnecting power generation system configured in this
way, the interconnection control unit 30 can detect a power outage
caused by an interruption of power supply from the utility power
system 10 based on a series of the predetermined number of matching
signals outputted from the phase comparator 24 and send a control
signal to the circuit breaker 22 to shut off the output of the
interconnecting inverter 14 from the utility power system 10, and
can decrease the rotational speed of the turbogenerator 32 to the
predetermined speed during the period between the detection of the
power outage and the shutoff of the utility power system 10.
To achieve the above object, according to a preferred embodiment of
the second aspect, there is provided an interconnecting power
generation system 1, wherein, as shown for example in FIG. 1, the
turbogenerator 32 recharges a battery 38 within the predetermined
period of time in response to the shutoff command.
To achieve the above object, according to a third aspect of the
invention, as shown for example in FIG. 1, there is provided an
interconnecting power generation system 1 connected in parallel to
a utility power system 10 and for supplying electrical power to an
interconnecting load 12, comprising: a turbogenerator 32 for
generating electrical power, an interconnecting inverter 14 for
linking electrical power generated by the turbogenerator 32 to the
utility power system 10; a voltage phase shift circuit 20 which
synchronizes the output voltage phase of the interconnecting
inverter 14 with the utility power voltage phase and monitors zero
crossings of the utility power voltage, and which, when a
predetermined number of zero crossings have been detected, shifts
the output voltage phase from the utility power voltage phase
during one cycle and shifts the shifted output voltage phase to the
utility power voltage phase during the following cycle; a circuit
breaker 22 for shutting off the output of the interconnecting
inverter 14 from the utility power system 10; a phase comparator 24
for comparing the voltage phase of the utility power system 10 and
the output voltage phase of the interconnecting inverter; and an
interconnection control unit 30 which detects a power outage caused
by an interruption of power supply from the utility power system 10
based on a series of a predetermined number of matching signals
outputted from the phase comparator 24 and sends a control signal
to the circuit breaker 22 to shut off the output of the
interconnecting inverter 14 from the utility power system 10, and
which sends a shutoff command to the turbogenerator 32 to stop the
operation of the turbogenerator 32 after allowing the turbine 36 to
rotate at the rated rotational speed for a predetermined period of
time.
In the interconnecting power generation system configured in this
way, the interconnection control unit 30 can detect a power outage
caused by an interruption of power supply from the utility power
system 10 based on a series of the predetermined number of matching
signals outputted from the phase comparator 24 and send a control
signal to the circuit breaker 22 to shut off the output of the
interconnecting inverter 14 from the utility power system 10, and
can send a shutoff command to the turbogenerator 32 to stop the
operation of the turbogenerator 32 after allowing the turbine 36 to
rotate at the rated rotational speed for the predetermined period
of time.
To achieve the above object, according to a preferred embodiment of
the third aspect, there is provided an, wherein, as shown for
example in FIG. 1, the turbogenerator 32 recharges a battery 38
within the predetermined period of time in response to the shutoff
command.
This application is based on the patent Application No.
JP-2002-357778, filed on Dec. 10, 2002 in Japan, the content of
which is incorporated herein, as part thereof.
Also, the invention can be fully understood, referring to the
following description in details. Further extensive applications of
the invention will be apparent from the following description in
details. However, it should be noted that the detailed description
and specific examples are preferred embodiments of the invention,
only for the purpose of the description thereof. Because it is
apparent for the person ordinary skilled in the art to modify and
change in a variety of manners, within the scope and spirits of the
invention. The applicant does not intend to dedicate any disclosed
embodiments to the public, and to the extent any disclosed
modifications or alterations may not literally fall within the
scope of the claims, they are considered to be part of the
invention under the doctrine of the equivalents.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a block diagram of an interconnecting power generation
system according to the first embodiment of the present
invention.
FIG. 2 is a waveform graph showing the output of the
interconnecting power generation system according to the first
embodiment of the present invention.
FIG. 3 is a flowchart illustrating passive independent operation
detection of the interconnecting power generation system according
to the first embodiment of the present invention.
FIG. 4 is a flowchart illustrating active independent operation
detection of the interconnecting power generation system according
to the first embodiment of the present invention.
FIG. 5 is a graph for illustrating the operation of the
interconnecting power generation system according to the second
embodiment of the present invention.
FIG. 6 is a graph for illustrating the operation of the
interconnecting power generation system according to the third
embodiment of the present invention.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
Description will be hereinafter made of the embodiments of the
present invention with reference to the illustrated examples. FIG.
1 through FIG. 6 are drawings for illustrating the embodiments for
carrying out the invention. In the drawings, those sections with
the same or similar reference numerals indicate the same or
equivalent items and redundant descriptions are omitted.
FIG. 1 is a block diagram of an interconnecting power generation
system according to a first embodiment of the present invention. An
interconnecting power generation system 1 comprises a rectifier 42
connected to a stator winding 40 of a turbogenerator 32, an
interconnecting inverter 14 connected to the rectifier 42 via a DC
bus 45, a smoothing capacitor 43 connected in parallel to the DC
bus 45, a battery 38 as electricity storage means connected to the
DC bus 45 via a DC/DC converter 44 as DC voltage converting means,
a circuit breaker 22 connected to the output of the interconnecting
inverter 14, and a control unit 2 connected individually to the
circuit breaker 22, an AC power line 46, the interconnecting
inverter 14, and the turbogenerator 32 for controlling the
interconnecting power generation system 1.
The control unit 2 comprises a phase comparator 24 connected to the
AC power line 46, a zero crossing monitor 16 connected to the AC
power line 46, a phase locked loop circuit (PLL) 49 as phase
synchronization loop means connected to the zero crossing monitor
16, a clock circuit 50 connected to the PLL 49, a voltage phase
shift circuit 20 connected to the zero crossing monitor 16 via a
counter 18 and connected to the clock circuit 50, a sine wave
generating circuit 51 connected to the voltage phase shift circuit
20, a pulse width modulation circuit 52 having an input connected
to the sine wave generating circuit 51 and an output (or outputs)
connected to the interconnecting inverter 14 and connected to the
phase comparator 24, and a control section 30 as an interconnection
control apparatus having an input connected to the phase comparator
24 and an output (or outputs) for outputting a circuit breaker
control signal to the circuit breaker 22 through a line 28 and a
turbine control command to the turbogenerator 32 through a line
34.
The turbogenerator 32 has a gas turbine 36 to which a permanent
magnet rotor (connected to the turbogenerator 32) is commonly
connected and which is rotated by combustion gas generated by
burning fuel with air, a stator winding 40 surrounding the
permanent magnet rotor connected to the gas turbine 36, and an
exhaust port 41 for discharging the combustion gas.
Description will be made of the operation of the interconnecting
power generation system 1 with reference to the block diagram of
FIG. 1. The interconnecting power generation system 1 is connected
in parallel to a utility power system 10 via the AC power line 46
and supplies AC electrical power with voltage and frequency of, for
example, 400V/50 Hz, 200V/50 Hz, or 100V/50 Hz to an
interconnecting load 12. It is needless to mention that the voltage
and frequency of the AC electrical power can be adjusted to those
of the electrical power supplied in the region where the
interconnecting power generation system 1 is installed.
When the turbogenerator 32 receives a start command from the
control section 30 through the line 34, DC electrical power is
supplied from the battery 38 to a start inverter (not shown), which
applies AC electrical power to the stator winding 40 to generate
torque in the permanent magnet rotor to start the gas turbine
36.
When the supply of fuel and air and the ignition condition are
controlled and the gas turbine 36 establishes self-operation, the
start inverter is shut off from the stator winding 40 and supplies
three-phase AC electrical power to the rectifier 42 connected to
the stator winding 40.
The rectifier 42 supplies DC electrical power to the DC bus 45
connected to its output charging the smoothing capacitor 43
connected in parallel to the DC bus 45 to stabilize the potential
of the DC bus 45. The rectifier 42 also supplies DC electrical
power to the interconnecting inverter 14 through the DC bus 45. In
this case, the DC electrical power supplied from the rectifier 42
may be boosted by a DC/DC converter (not shown) may be supplied to
the interconnecting inverter 14.
The interconnecting inverter 14 has three pairs of IGBT (Insulated
Gate Bipolar Transistor) switching transistors which are driven
complementarily, and generates pulse-width-modulated sine wave AC
voltage which follows the voltage phase of the utility power system
10 by switching on/off the DC voltage supplied from the DC bus 45
with a pulse width modulation (PWM) control signal.
The phase comparator 24 and the zero crossing monitor 16 are
connected in parallel to the AC power line 46. When the circuit
breaker 22 is on state (closed), the phase comparator 24 detects
the voltage phase of the utility power system 10 which appears in
the AC power line 46 and receives an output signal for driving the
interconnecting inverter 14 from the pulse width modulation circuit
52. The phase comparator 24 compares the detected voltage phase of
the utility power system 10 and the output signal from the
interconnecting inverter 14 and compare the output voltage phase of
the interconnecting inverter 14 and the voltage phase of the
utility power system 10 in a pseudo manner. The comparison result
and a voltage phase signal of the AC power line 46 are outputted to
the control section 30 through a line 26.
The control section 30 controls the whole interconnecting power
generation system 1. The control section 30 can prevent the
interconnecting power generation system 1 from operating
independently since the control section opens (shuts off) the
circuit breaker 22 by sending a control signal to the circuit
breaker 22 through the line 28 to isolate the interconnecting
inverter 14 from the utility power system 10 when the voltage phase
of the utility power system 10 is determined to have a frequency
which exceeds or falls short of the frequency of the output voltage
phase of the interconnecting inverter 14 by approximately 2% or
greater based on the comparison result by the phase comparator
24.
For example, when no matching signal (or disagreement signal) is
outputted from the phase comparator 24 within a period when the
voltage phase of the utility power system 10 is to be matched with
the output voltage phase of the interconnecting inverter 14 or when
no matching signals (or disagreement signals) are outputted for a
predetermined number of times in sequence, the control section 30
determines that the frequency of the voltage of the utility power
system 10 is excessively high or low, and opens (shuts off) the
circuit breaker 22 to isolate the interconnecting inverter 14 from
the utility power system 10. The interconnecting power generation
system 1 configured in this way can be thus isolated within at most
several hundreds ms, preferably within 0.2 seconds.
When the circuit breaker 22 is on and the output voltage phase of
the interconnecting inverter 14 is same with the voltage phase of
the utility power system 10, the zero crossing monitor 16 monitors
zero crossings of the voltage phase of the AC power line 46 via a
line 47.
The zero crossing monitor 16 monitors the zero crossing timing at
which the voltage waveform of the AC power line 46 passes a
reference potential (ground potential) and outputs a zero crossing
detection signal to the counter 18 every time it detects a zero
crossing. Counting the zero crossing detection signals allows
determining one cycle of the voltage waveform of the AC power line
46. For example, three zero crossing detection signals can be
counted as one cycle of a sine wave voltage waveform.
The zero crossing monitor 16 sends a waveform signal to the PLL 49
through the line 48. The PLL 49 is an electronic circuit for making
the frequency of an output signal to coincide with the frequency of
an input signal or a reference frequency. For example, the PLL 49
detects the phase difference between the input signal and the
output signal and generates a signal having a frequency accurately
synchronized with the frequency of the input signal or the
reference frequency by controlling a VCO (an oscillator that
controls the frequency according to the voltage) or a loop of its
internal circuit.
The voltage phase shift circuit 20 is configured to divide the
frequency of the clock circuit 50 so that it can make the output
voltage phase of the interconnecting inverter 14 coincide with the
voltage phase of the utility power system 10 according to the
output of the PLL 49. The voltage phase shift circuit 20 also
receives a voltage phase shift signal from the counter 18 when it
has counted a predetermined number of zero crossings or when it has
counted a zero crossings after an internal timer (not shown) has
reached a predetermined period of time. In response to the voltage
phase shift signal, the voltage phase shift circuit 20 changes the
frequency division ratio of the clock circuit 50 (delays or
advances the phase of the clock), with the zero crossing timing as
a starting point, and outputs a changed clock signal to the sine
wave generating circuit 51.
The sine wave generating circuit 51 sends a sine wave with a
shifted voltage phase to the pulse width modulation circuit 52. The
pulse width modulation circuit 52 drives the interconnecting
inverter 14 to shift the output voltage phase from the voltage
phase of the utility power system 10.
For example, the voltage phase shift circuit 20 receives a voltage
phase shift signal from the counter 18 every 100 ms and sets the
frequency division ratio of the clock circuit 50 with the zero
crossing timing as a starting point to cause a phase delay (minus
phase shift) in response to the voltage phase shift signal. After
the output voltage phase of the interconnecting inverter 14 has
been shifted during one cycle, the voltage phase shift circuit 20
resets the frequency division ratio of the clock circuit 50 to
cause a phase advance (plus phase shift) to return the output
voltage phase to the initial state, whereby one phase shifting
operation is completed.
When the utility power system 10 is normal during the frequency
shifting operation, the impedance of the utility power system 10 is
so low that changes in the output voltage phase of the
interconnecting inverter 14 do not affect the voltage phase of the
AC power line 46. Thus, the phase comparator 24 does not detect the
shift in the voltage phase.
On the other hand, in case that the utility power system 10 is
interrupted, even when the power outputted from the interconnecting
inverter 14 and the power consumed by the interconnecting load 12
are balanced, including active power and reactive power, the
shifted output voltage phase from the interconnecting inverter 14
appears as it is in the AC power line 46 with the interconnecting
load 12. Thus, the control section 30 can compare the voltage phase
received from the phase comparator 24 with the normal output
voltage phase to detect a change in the voltage phase. In this
case, the phase shift amount is determined based on the time
difference in the zero crossing timing of the voltage phase.
Namely, the phase is shifted reliably for a period of two cycles of
an advanced phase and a delayed phase, with the zero crossing
timing as a starting point. Thus, when a power outage in the
utility power system occurs, for example, in contrast to the case
where the phase is shifted to be advanced only for one cycle, which
may result in the phase not to be shifted if the phase is
oppositely shifted to be delayed according to the load condition
and may result in the inability to detect the power outage, the
interconnection control unit 30 can detect the power outage
irrespective of the load condition using the comparison result of
the phases during the period of two cycles of the advanced phase
and the delayed phase.
Thus, when the delayed or advanced voltage phase is detected during
the period of two cycles, it is determined that the power supply is
interrupted and a circuit breaker control signal is sent through
the line 28 to open the circuit breaker 22, whereby the
interconnecting power generation system 1 can be isolated from the
utility power system 10. Thus, it is possible to prevent
independent operation of the interconnecting power generation
system 1.
Since the counter 18 outputs a voltage phase shift signal every 100
ms, it maybe determined that the power supply is interrupted when
the delayed or advanced voltage phase appear during the period of
two cycles are detected at least twice in a row. The
interconnecting power generation system 1 can be isolated within at
most several hundreds ms, preferably within 0.5 seconds in this
way.
In the description above, the delayed or advanced voltage phase is
detected during the period of two cycles. However, the phase
difference may also be detected for a period of one half or full
cycle (in this case, the phase difference can be detected during
the cycle in which the phase is changed into the same direction as
the direction of the phase change according to the load state
predetermined or in which the phase change according to the load
state is little, for example). Instead, an increase or decrease in
the frequency which may occur during the period of two cycles may
be detected for achieving the same effect. Although description has
been made above of a method in which the phase is shifted over two
cycles, it will be appreciated that another method may be used for
achieving the same effect in which the phase is shifted over more
than two cycles for the detection. The order of the advanced and
delayed phases during the period of two cycles may be reversed.
Although the interconnecting power generation system is configured
using a hardware logic as described above in this embodiment, the
present invention is not limited to the above configuration. For
example, the same effect can be obtained when the phase comparison,
zero crossing monitoring, pulse width modulation and digital PLL
are performed by software processing using a microcomputer or a
digital signal processor and the processing operation is performed
after converting the voltage phase of the AC power line 46 into a
digital signal by an A/D converter (not shown).
When the control section 30 detects any one of an under-frequency
or over-frequency condition or a power outage, the control section
30 sends a turbine control command through the line 34 to decrease
the rotational speed of the gas turbine 36. Since the gas turbine
36 is operated at a rotational speed which is lower than the rated
speed, the rotational speed of the gas turbine 36 does not increase
to the absolute rated speed with the turbogenerator 32 at no-load
condition even when the circuit breaker 22 is opened immediately
after (approximately 0.2 to 0.5 seconds after) the detection to
isolate the interconnecting power generation system 1 from the
utility power system 10.
The control section 30 also sends a shutoff command to the
turbogenerator 32 through the line 34 to control the rotational
speed of the gas turbine 36 to be returned to the rated speed.
Then, the control section 30 allows the gas turbine 36 to rotate at
the rated speed for a predetermined period of time and then stops
the operation of the turbogenerator 32. Since the rotational speed
of the gas turbine 36, which have once increased because of the
no-load operation, returns to the rated speed, the circuit breaker
22 can be closed (turned on) to link the interconnecting power
generation system 1 with the utility power system 10 again when the
normal power supply is restored after a short period of work during
the power outage.
When the power outage continues and the work during the power
outage continues until after the predetermined period of time has
elapsed, the turbogenerator 32 is stopped leaving the circuit
breaker 22 opened (turned off). Thus, the auxiliaries can be
completely cooled down.
When the control section 30 detects any one of an over-frequency or
under-frequency condition or a power outage, the control section 30
controls the battery 38 to be charged from the DC bus 45 through
the DC/DC converter 44. The charging time of the battery 38 is
preferably set to a period of any length by the time the
turbogenerator 32 is stopped.
FIG. 2 is a waveform graph showing the output of the
interconnecting power generation system 1 according to the first
embodiment of the present invention. The interconnecting power
generation system outputs a voltage waveform 56 from the
interconnecting inverter to the AC power line 46. The voltage
waveform 56 shown by a solid line in the graph indicates any one of
three-phase AC outputs (u, v, w). The voltage waveform 56 shown by
a broken line indicates a normal AC waveform (non-shifted
waveform).
The control section 30 (see FIG. 1) receives a shift signal 57 from
the counter 18 and monitors the comparison result between the phase
of the voltage waveform from the interconnecting inverter 14 shown
by a solid line and that of the utility power system voltage
waveform shown by a broken line. The voltage phase shift circuit 20
(see FIG. 1) synchronizes the frequency FHz and phase of the
voltage waveform 56 as the output of the interconnecting inverter
14 with the frequency and phase of the utility power voltage and
monitors zero crossings of the utility power voltage. When a
predetermined number of zero crossings, ten zero crossings in the
case of 50 Hz, for example, are detected or when a zero crossing is
detected after the internal timer has reached 100 ms, for example,
with the zero crossing as a starting point, the voltage phase shift
circuit 20 delays the output voltage phase of the voltage waveform
56 within one cycle (20 ms) (which results in the frequency thereof
to be shifted from the frequency F of the utility power voltage to
the frequency (F+.DELTA.f)). Then, the voltage phase shift circuit
20 advances the output voltage phase of the voltage waveform 56
within the next one cycle (20 ms) (which results in the frequency
thereof to be shifted from the frequency F of the utility power
voltage to the frequency (F-.DELTA.f)). In this way, the control
section 30 can perform frequency shifting, which results from the
phase shifting starting every 100 ms at the zero crossing point.
The period of two cycles starting at the zero crossing point,
during which the phase of the voltage waveform is changed, will be
referred to as frequency shifting period.
The illustrated voltage waveform 56 is synchronized with the
frequency F of the utility power voltage except for the frequency
shifting period. A frequency shifting period is started at a zero
crossing point 55 which appears immediately after the falling edge
58 of the shift signal 57 and the frequency of the voltage waveform
56 is increased by .DELTA.f (Hz). During the frequency shifting
period, the shift signal 57 is activated and a zero crossing point
53 which appears one cycle after the zero crossing point 55 is
detected, and data on the shifted waveform with the increased
frequency is captured. Since the voltage waveform 56 shown by a
solid line is advanced in phase with respect to the normal voltage
waveform shown by a broken line, the utility power system 10 is
interrupted and the AC power line 46 is also interrupted. When the
phase shift of the zero crossing point 53 is detected, the control
unit 2 can control the circuit breaker 22 to be opened.
Then, the frequency of the voltage waveform 56 is decreased by
.DELTA.f (Hz) at the zero crossing point 53 to return it to the
normal frequency F. A zero crossing point 54 which appears one
cycle after the zero crossing point 53 is detected and data on the
shifted waveform with the decreased frequency is captured. The
frequency F of the voltage waveform 56 at this point of time is
synchronized with the utility frequency.
A frequency shifting period as described above is started again in
response to a falling edge 58a which deactivates the shift signal
57, which has been activated, 100 ms after the falling edge 58 of
the shift signal 57. Likewise, data on the shifted waveform with
the increased frequency is captured at a zero crossing point 53a to
detect a power outage in the AC power line 46. In this embodiment,
the circuit breaker 22 may be opened not at the first detection of
the power outage but in response to the second detection of the
power outage. By detecting power outages in sequence as described
above, there can be provided an interconnecting power generation
system with high reliability which can avoid independent
operation.
Then, in order to return the frequency of the voltage waveform 56
to the normal frequency F, the frequency of the voltage waveform 56
is decreased by .DELTA.f (Hz) at the zero crossing point 53a. A
zero crossing point 54a which appears one cycle after the zero
crossing point 53a is detected and data on the shifted waveform
with the decreased frequency is captured. The frequency F of the
voltage waveform 56 at this point of time is synchronized with the
utility frequency. Then, a frequency shifting period can be started
in response to a falling edge 58b of the shift signal 57 100 ms
after the falling edge 58a.
Although the voltage waveform 56 has been described above as a
waveform at the time of a power outage shown by a solid line, when
the utility power system 10 is normally supplying electrical power,
the frequency of the voltage waveform 56 in the AC power line 46 is
changed to the frequency of the voltage waveform shown by a broken
line even if a shifted voltage waveform is outputted from the
interconnecting inverter 14.
FIG. 3 is a flowchart illustrating passive independent operation
detection of the interconnecting power generation system according
to the first embodiment of the present invention. When proceeding
from the start step to the step 60, the interconnecting power
generation system performs passive independent operation detection.
When completing the independent operation detection, the process
proceeds to the step 61, where the interconnecting power generation
system performs active independent operation detection. At the step
61, it is determined whether the detected frequency of the voltage
which appears in the AC power line 46 during the frequency shifting
period is higher or lower than the reference frequency. For
example, when the utility frequency is 50 Hz and the frequency
shift amount is set to 1 Hz, an over-frequency or under-frequency
can be detected with a detection level of .+-.2%.
If the determined result is negative (NO), the process proceeds to
the step 62, where an active timer is initialized (reset to zero).
Then, the process proceeds to the step 63, where the process is
ended. If the determined result is positive (YES), the process
proceeds to the step 64, where it is determined whether or not an
active detection time has elapsed.
When the detection time has elapsed, namely when the determined
result is positive (YES), the process proceeds to the step 65,
where passive independent operation is detected and the circuit
breaker 22 is opened. Then, the process proceeds to the step 63,
where the process is ended. When the determined result is negative
(NO) at the step 64, the process proceeds to the step 66, where the
active timer is incremented. Then, the process proceeds to the step
63, where the process is ended.
By repeating the passive independent operation detection process
described above, an over frequency or an under frequency can be
detected at any times with a detection level of .+-.2%. When the
detection level of the frequency shift is set to 1/2 of the shift
frequency, for example, when the frequency of the utility power
system 10 is 50 Hz and the frequency shift amount is set to 1 Hz, a
frequency shift is detected when the frequency is 50.5 Hz or higher
at the time when the frequency is increased. Also under the same
conditions, a frequency shift is detected when the frequency is
49.5 Hz or lower at the time when the frequency is decreased.
FIG. 4 is a flowchart illustrating active independent operation
detection of the interconnecting power generation system according
to the first embodiment of the present invention. The
interconnecting power generation system starts active independent
operation detection in the step 70. Then, the process proceeds to
the step 71, where it is determined whether or not it is during the
frequency shifting period.
If the determined result is positive (YES), the process proceeds to
the step 74, where the internal PLL is advanced to increase the
frequency. Then, the process proceeds to the step 73, where the
process is ended. If the determined result is negative (NO), the
process proceeds to the step 72, where it is determined whether or
not the frequency was increased (plus shift) in the previous
frequency shifting operation. If the determined result is positive
(YES), the process proceeds to the step 75, where the internal PLL
is delayed to decrease the frequency. Then, the process proceeds to
the step 73, where the process is ended. When the determined result
is negative (NO) at the step 72, the process proceeds to the step
73, where the process is ended.
The active independent operation detection process is repeated to
shift the frequency at intervals of about 100 ms. The voltage
waveform which appears in the AC power line 46 is monitored so that
a power outage in the utility power system 10 can be detected.
FIG. 5 is a graph for illustrating the operation of an
interconnecting power generation system according to a second
embodiment of the present invention. In the interconnecting power
generation system, when the control section 30 sends a shutoff
command 78 to open the circuit breaker 22, the turbogenerator 32
decreases the supply of fuel and air to decrease the rotational
speed 76 of the gas turbine 36 within 30 seconds from the rated
rotational speed to a low rotational speed in preparation for
stopping it.
The control section 30 sends a charging start command 79 for
controlling the DC/DC converter 44 to charge the battery 38. While
the gas turbine 36 is rotating at the decreased speed, the charging
of the battery 38 is complete (80) within about 15 minutes. Then,
the control section 30 stops the supply of fuel and air to the gas
turbine 36 to stop the combustion in the gas turbine 36.
Cooling of the auxiliaries and circulating oil is complete (81)
about 10 minutes after the battery charging has been complete (80),
and the gas turbine 36 can be stopped completely. When the shutoff
command 78 is outputted, the turbine exhaust temperature 77 is the
rated value. Then the rotational speed of the gas turbine 36
decreases in response to the shutoff command 78 to increase the
turbine exhaust temperature 77, but the increased temperature is
still within a permissible value. Then the combustion in the gas
turbine 36 is stopped and the turbine exhaust temperature 77
gradually decreases and the cooling is complete (81).
FIG. 6 is a graph for illustrating the operation of an
interconnecting power generation system according to a third
embodiment of the present invention. The interconnecting power
generation system sends a turbine deceleration command to the
turbogenerator 32 when the control section 30 has detected a power
outage (82). The turbogenerator 32 decreases the supply of fuel and
air to decelerate the gas turbine 36 to a lower rotational speed
than its rated speed.
The control section 30 sends a shutoff command 78 within about 1
second after the power outage detection (82) to open the circuit
breaker 22 isolating the interconnecting power generation system
from the utility power system 10. Since the turbogenerator 32 is
put into a no-load operating condition by the isolation, the
rotational speed of the gas turbine 36 increases to a trip level 84
as indicated by B. However, the rotational speed does not reach an
overspeed 83, such as when the isolation is made when the gas
turbine 36 is operating at the rated speed as indicated by A
because of lower rotational speed of the gas turbine 36.
The turbogenerator 32 controls the supply of fuel and air to return
the rotational speed of the gas turbine 36 from the trip level 84
to its rated speed. After the rotational speed of the gas turbine
36 has been returned to the rated speed, charging of the battery 38
is started (79). The charging of the battery 38 is complete in
about 15 minutes (80).
In this embodiment, the turbogenerator 32 is operated for about
another 20 minutes, during which the voltage of the AC power line
46 is monitored to detect power restoration of the utility power
system 10. When the power outage continues for 20 minutes or
longer, the combustion in the gas turbine 36 is stopped (81) and
the turbine speed is gradually decreased until the turbogenerator
stops completely (81).
When power restoration of the utility power system 10 is detected
after the charging of the battery 38 has been completed (80) as
shown by the dot-dash line C, rated operation is continued and the
interconnecting power generation system 1 and the utility power
system 10 can be reconnected by synchronizing the frequency of
output from the interconnecting power generation system 1 with that
of the utility power system 10 and closing the circuit breaker 22.
The reason why the gas turbine 36 is operated continuously is to
prevent the gas turbine 36 from starting and stopping
frequently.
Thereby, the interconnecting power generation system can avoid
independent operation by detecting an abnormality in the utility
power system 10 and can prevent damage to and deterioration of the
turbogenerator 32.
The interconnecting power generation system of the present
invention is not limited by the above examples illustrated in the
drawings, and it will be appreciated that variations and
modifications may be made without departing from the spirit and
scope of the present invention.
As has been described above, according to the invention of claims 1
to 6, there is provided an interconnecting power generation system
which can detect an abnormality in the utility power supply and can
be isolated from the utility power a system and can prevent damage
to a turbogenerator.
* * * * *